A common misconception is that a climate "normal" describes the
"typical" state of the atmosphere.
"Normal" is simply a 30-year arithmetic mean, computed once per decade. The
precipitation normals data presented in the maps below summarize the observation period
1971-2000. These values are benchmarks to be used throughout this decade as a
measure of central tendency. Normals data can be useful in placing ongoing
weather conditions in historical context. Additionally, normals data offer an
excellent tool for describing climate variability across space. Clicking on any
of the maps below will bring the user to a page that provides a larger version of
the normal precipitation map, as well as links to *.zip files containing the map in a variety
of formats (*.gif, *.wmf, ESRI ArcView, EPPL7).